GB464788A - Improvements in or relating to modulated carrier wave transmitters and apparatus for use therewith - Google Patents

Abstract

464,788. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and TRINGHAM, W. S. L. Oct. 24, 1935, No. 29405. Addition to 428,700. [Class 40 (v)] In a modulation monitoring-installation for radio and like transmitters of the kind d in which a cathode-ray tube is switched in turn to various stages of the transmitter, an amplifier is provided between the switch and the cathode-ray tube, and the modulated carrier wave is rectified by a rectifier situated adjacent the switch. In the circuit shown, the switch S comprises two perpendicular rotary arms A1, A2 movable into three positions over the twelve contacts. According to the position of the switch arms, voltages are received from three different stages of the transmitter and are applied across the grid and cathode of an amplifier V, the plate circuit of which is coupled to the cathoderay indicator. Voltages from the pre-modulation stage may be taken from a tapping on the anode resistance AR of that stage and fed to the switch contacts through a high-frequency cable C. Similarly, voltages from the modulator stage are fed through a cable C1. The modulated carrier stage is connected by a cable C2 to a flatly-tuned circuit K2, L2, connected in the circuit of a diode rectifier V1, the load resistance R1 of which is connected to the switch contacts. In a modification, the modulated carrier is taken from the aerial feeder by bridging that feeder at a point about one-eighth of a wave-length from its input end by a small condenser in series with a low resistance from across which the carrier voltage is taken to the rectifier V1. This latter arrangement may also be used for feeding a local monitoring television reproducer. The rotary switch may be replaced by cam-operated switch arms, Figs. 2 and 3 (not shown). The apparatus enclosed in the dotted line is situated at the monitoring and switching point.